C language file positioning: Use of fseek () and ftell () Functions

The fseek function is used to set the current read/write location of a file:

Function prototype: int fseek (File * FP, long offset, int origin );
Function: moves the FP file read/write position pointer to the specified position.

 

Fseek (FP, 20, seek_set );

// Indicates that the pointer to the read/write position of the FP file is removed 20 bytes after the file starts.

The ftell function is used to obtain the current read/write location of a file;
Function prototype: Long ftell (File * FP)
Function: Obtain the current read/write position of the stream file. The returned value is the number of bytes that the current read/write position deviates from the file header.

 

Ban = ftell (FP );

// Obtain the current read/write location of the file specified by FP and pass the value to the variable ban.

Comprehensive application of fseek and ftell functions:
Analysis: You can use the fseek function to move the position pointer to the end of the file, and then use the ftell function to obtain the number of bytes from the file header. This number is the length of the file.

# Include <stdio. h> main () {file * FP; char filename [80]; long length; printf ("input the file name:"); gets (filename ); fp = fopen (filename, "rb"); If (FP = NULL) printf ("file not found! /N "); else {fseek (FP, ol, seek_end); length = ftell (FP); printf (" the file length % 1D Bytes/N ", length ); fclose (FP );}}